1. Field of the Invention
The present invention relates to fuel vapor processing apparatus.
2. Description of the Related Art
A fuel vapor processing apparatus is known that includes a vapor passage for introducing fuel vapor, which is produced within a fuel tank of an automobile, into a canister, an atmospheric-side opening and closing device provided to the canister, a negative pressure generating device for generating a negative pressure, and a recovery passage communicating between the negative pressure generating device and the canister. The negative pressure generating device can operate for recovering fuel vapor stored within the canister into the fuel tank via the recovery passage.
This type of fuel vapor processing apparatus is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2002-235608. As shown in FIG. 8, a fuel vapor processing apparatus 100 disclosed in this publication includes a vapor passage 104 for introducing fuel vapor, which is produced within a fuel tank T, into a canister 103, an atmospheric-side opening and closing valve 105 capable of opening the canister 103 into the atmosphere, a negative pressure generating device 107 disposed within the fuel tank T for generating a negative pressure, and a recovery passage 108 communicating between the negative pressure generating device 107 and the canister 103.
Fuel vapor may be produced within the fuel tank T, for example, during parking of an automobile and may be introduced into the canister 103 via the vapor passage 104. The fuel vapor is then adsorbed by an adsorption material (such as activated carbon) that is disposed within the canister 103. Therefore, it is possible to prevent the fuel vapor produced within the fuel tank from being leaked into the atmosphere.
In addition, the fuel vapor stored within the canister 103 may be drawn into the fuel tank T via the recovery passage 108 when the negative pressure generating device 107 is operated during driving of the automobile. The fuel component of the fuel vapor introduced into the fuel tank T is then recovered into the fuel.
However, according to the fuel vapor processing apparatus of the above publication, the internal pressure within the canister 103 becomes negative during recovering of the fuel vapor, and therefore, gas contained within the fuel tank T may flow from the vapor passage 104 into the canister 103. In other words, the adsorption material disposed within the canister 103 is purged by the gas contained within the fuel tank T. Because the gas contained within the fuel tank T includes fuel vapor, it is hard to effectively desorb the fuel vapor from the adsorption material by using the gas for purging.
In order to solve this problem, it may be possible to open the atmospheric-side opening and closing valve 105 for introducing external air into the canister 103. However, if external air flows into the canister 103, the external air may be drawn into the fuel tank T via the recovery passage 108 to cause another problem of increase in the internal pressure of the fuel tank T.
Therefore, there is a need in the art for a fuel vapor processing apparatus that can inhibit increase in an internal pressure of a fuel tank without accompanying decrease in the recovering efficice of fuel vapor.